The present invention relates generally to liquid crystal displays, and more particularly, to a method and apparatus for pre-assembling optical components for use with a liquid crystal display.
Assembling various optical components typically associated with liquid crystal displays (LCDs) requires a process which is essentially defect free, resulting in high yields. The various optical components used in conjunction with LCDs include both rigid optical components and flexible optical components. Rigid optical components can be, for example, glass plates, diffusers, compensators and heaters. Flexible optical components can be films such as polarizers, retarders, and dry film adhesives. The high costs of LCDs and these related optical components makes it very important to eliminate or greatly reduce waste. Further, defects in the assembly process can significantly effect the performance of an LCD.
A common defect which manifests itself during assembly of LCD optical component stack-ups is misalignment between optical axes of various components. For example, the absorption axis of a polarizer material must be aligned, within a very low tolerance, with the rub axis on the LCD substrate. To obtain the contrast necessary for avionics displays, the total misalignment must be no greater than 1 degree. Current assembly techniques result in misalignment in excess of 2 degrees, and as such, are inadequate for achieving the necessary alignment tolerances.
A number of assembly techniques exist in the prior art. Each of these techniques introduces one or more defects into the LCD stack-up. These defects include strain on the LCD, loss of adhesion between optical components, bubbles formed between optical components, stress fractures occurring in the adhesive materials, discoloration of the adhesive materials, high reflectance due to poor index matching of the adhesive material to the optical components, and birefringence of the adhesive materials causing undesirable effects in the display output such as Newton rings and loss of contrast. Consequently, there is a need for a low cost assembly process which eliminates these defects to provide a high yield of optical component assemblies which exhibit stability through environmental testing under extreme conditions of temperature, humidity and vibration.